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#135356 - 01/01/03 02:12 PM It's a small world
C-H Offline
Member
Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
I cut and pasted this from an Israeli electrian's site. Nice to know that everyone has the same problems
--------------

Customer: Hello is that the electrician ?
Listen, the new circuit breakers that you just put in keep tripping. The old fuses never blew !

EDS: Ah ! thats because someone had already replaced the old fuses with coffin nails which meant that instead of the old fuses protecting the house wiring, the wiring was protecting the fuses !

Customer: But it worked and I could run the washing machine at the same time as the dryer, the dishwasher, the stove and all the room heaters !!! Can’t you put a ‘stronger’ circuit breaker in the box ?

EDS: Maybe you should have kept the old fuses and replaced all the wiring instead !

Look, for safety the fuses or circuit breakers MUST be weaker than the wire in it’s circuit. That way if there’s a problem, the fuse will go before the wire starts burning or the the switch contact goes. The thickness of the wiring determines the size of the fuse that has to be installed. There have been countlesss cases of fires in electrical boxes caused by overloaded circuits or faulty fuses.

Customer: So what can I do with my washing machine and dryer ?

EDS: In new flats that are wired correctly, each device will have it’s own correctly rated breaker. In old houses you’ll probably have to run one machine after another or install a new heavy duty circuit from the main fuse-panel to one of the machines. Also, dryers usually have a half-power setting.
(any resemblance to actual customers is purely coincidental !)
------

Some interesting information about the Israeli wiring on the site btw:
http://members.tripod.com/~eds_engineering/
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#135357 - 01/02/03 03:54 AM Re: It's a small world
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Some interesting items on that site. Did you see the part about their PoCo not wanting to provide a single-phase supply over 40 amps?
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#135358 - 01/02/03 05:00 AM Re: It's a small world
C-H Offline
Member
Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Yes, I did. I have a standards proposal in this field too, but I'll take that some other day.
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#135359 - 01/02/03 09:58 PM Re: It's a small world
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8560
Loc: SI,New Zealand
C-H,
Seen this God knows how many times,
especially with replacing Pillar Box(Mains) fuses(HRC),with houses protected by RWF sub-
circuits, if it blows again, just put a bigger fuse wire in the holder, most home-owners over here, do not care about Co-ordination of protective devices, hence, the Power board, turning up when the whole house has gone dead.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
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#135360 - 01/04/03 09:41 PM Re: It's a small world
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8560
Loc: SI,New Zealand
Sorry C-H,
I have managed to kill another subject.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin
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#135361 - 01/05/03 03:53 AM Re: It's a small world
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Quote:
I have a standards proposal in this field too,


Don't be shy -- Let's hear them!
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#135362 - 01/05/03 12:38 PM Re: It's a small world
C-H Offline
Member
Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
I don't think I have posted this before.

Read the EDS article first, to see the background. I have thought of this before: The EDS article speaks of 3x25A, but some countries (yeah, guess which ) use 3x16A.

Got a phone call from a friend yesterday, who had this problem. "The cooker rings aren't working nor is some of the heating." "Replace the broken main fuse"

It's impossible to balance a normal houshold on a small 3-ph system. No matter how you place the dishwasher, kitchen counter sockets, washing machine it only takes someone using the dishwasher, kettle and the oven to blow one main fuse. Sure, you can move them around but the only result is the fuse blowing when the washing machine is used instead.

Now this wasn't so bad if it weren't for the combination of phase-to-phase loads and single pole fuses which means that when a fuse has blown, the voltage is dancing around uncontrollably. When you turn on the cooker, the kitchen lamp goes on... Electronic equipment find itself on say 150V rather than 230V and go nuts. I've set of a fire alarm this way once.

On the other hand: Single phase is a very inefficient way of moving power and it causes problems with load balancing for the power company.

Striking a balance would seem nice, so here goes:

A 3-ph connection of less than 50A per phase shall count as single phase service of 2 x phase rating. For example a 3x50A service counts as one single phase 100A service. At the other extreme, a 3x16A service counts as one 32A single phase service.

In new install. Single phase should be used for up to 63A max. and three-phase from 3 x 32A and up. {Jeering from the Brits: Why not 100A? From the Germanics: Heretic! Single phase is stone age! }

Balancing 3x32A is possible as it allows two continous 16A loads to be run simultanously on one phase. Plus the kettle for a few minutes. 32A is enough even to run a normal sized cooker. On the other hand, 63A is still easy to wire and main breakers, RCD:s etc. easily fit a normal panel (16 mm2 cable).

Now: There is one more point for my system. The copper needed to run a 3x32A cable 3P+PEN is 4x6 mm2 = 24 mm2. 63A P+PEN requires 2x16 mm2 = 32 mm2. The difference in cost is probably outweigth by the more expensive 3-ph panel.

A 100A single phase serious is just silly, IMO, since balancing a 3x50A service won't be a problem. And by then you are using an incredible amount of copper: 2x25 mm2 or 4x10mm2, which probably makes the cost of a 3-ph panel less than the savings on the cable.

Next, I argue that main fuse/breakers shouldn't blow/trip unless in extreme and thus rare cases. Furthermore, I would like to mandate three pole breakers on 3-ph circuits to prevent uncontrolled voltages. These ideas, I think go hand in hand.

Hutch, can I use your bomb shelter?

[This message has been edited by C-H (edited 01-08-2003).]
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#135363 - 01/05/03 03:08 PM Re: It's a small world
Hutch Offline
Member
Registered: 05/27/02
Posts: 383
Loc: South Oxfordshire, UK
I assume this is a 230/380V system. What phase to phase loads do you anticipate - stove, water heater ... ?

Wouldn't it be simpler to keep things phase to neutral or are you looking for savings on copper and less voltage drop on these higher power items.

As for the po-co, surely the statistics of large numbers will balance out the demand on all phases without seeking each customer's help.

My workshop would be nicer with domestic 3 phase on hand Shelter's open if you need it!
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#135364 - 01/05/03 07:17 PM Re: It's a small world
pauluk Offline
Member
Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
You make an excellent point C-H. I've come across 3x16A 3-phase in some French houses, and wondered how one would best go about connecting 4 heavy loads. I know of some Brits who have encountered problems with this in their French holiday homes, in many cases because they not only want washers, dryers, etc. but also because they are so attached to their trusty electric kettles!

Certainly specifying 3-phase as a minimum of 3x32A makes the load balancing much easier, although this would still cause problems for the big "instant" showers (I don't think these are so common in Continental Europe, are they?).

With regard to load balancing from the PoCo's perspective, I don't see that having single-phase residential services of up to 100A makes that task any more difficult in most cases. I suppose the only extra work might be to keep records of which houses are fed from which phase.

Although all U.K. distribution in towns and village centers is 4-wire from 3-ph transformers, in the case of rural areas it's not uncommon to see one or two houses standing on their own served by a single-phase xfmr which is fed on a 2-wire spur line (i.e. HV spur is 2 phases from the standard 11kV delta). I imagine that to install a 3-wire line and 3-ph xfmrs in all these places would increase the costs significantly.
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#135365 - 01/06/03 10:45 PM Re: It's a small world
C-H Offline
Member
Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Yes, Hutch, I agree: Appliances should be neutral to line. That way they would work on both 3-ph and single ph systems. But, this is not the way it is today.

Paul:
I don't think balancing the transformer isn't a problem, but balancing the phases in a cable suppling a small number of houses could be.

Big instant shower: I know Brits use 40-60A single phase power showers, but then again you still have single glazed windows, whereas we have triple or even quadruple window panes. The Germans use 3x25A or even 3x30A power showers... (The largest size is 27 kW/ 3x40A, IIRC) Apparently, they sometimes don't bother with suppling old flats with hot water. Instead the flat gets one h**l of an electric supply. (Like 3x50A)

Swedes prefer to have things like heating centralized: Stockholm has not only centralized heating from power plants in and around the city, but also centralized airconditioning. Yes, really: There are huge pipes in the ground with coolant!

(Gothenburg runs the airconditioners off the hot water. Sounds crazy, but they have a lot of waste heat in the summer. This heat is turned into cooling by the airconditioners in buildings.)

BTW: Do other cities have street heating? Central part of Stockholm does and it is a blessing in winter.

[This message has been edited by C-H (edited 01-07-2003).]
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